The gliding characteristics of a ski are determined by a number of factors, i.e. by its bending resistance, its flexibility over the whole length of the ski, its torsional strength etc. Furthermore, the structure of the running surface--usually provided with one or more guiding grooves--has an essential influence on the guidance of the ski, i.e. on its directional stability as well as on its turnability.
Conventionally, a guiding groove starts in the portion next to the tip of the ski and extends longitudinally and with constant cross-section over the rest of its running surface, i.e. to its rear end; the groove generally has an arcuate or trapezoidal cross-section and may be either pressed into the running surface or milled out of it.
The number of such grooves and the shape of their cross-sections determine their guiding effect; thus, an increasing number of guiding grooves as well as an increase in their depth or in the flank angle of their cross-section improves the directional stability of the ski but impairs its turnability.
It has already been proposed to subdivide the running surface of the ski into several portions of different longitudinal profiling and consequently of different guiding effect. Swiss Pat. No. 161,592, for example, teaches that the central groove extending continuously over the front, middle and rear portions of the ski is to be flanked only in the middle portion by several additional smaller grooves designed to achieve good guidance when skiing straight downhill as well as good maneuverability on Christiania turns.
In the meantime, in the field of Alpine skiing, the conditions of the ski slopes have changed along with skiing technique and the structure of the ski has undergone an important development.